1. FIELD OF THE INVENTION
This invention relates to the material handling field in general, and more particularly, to a planar, low cost air pallet material handling system permitting heavy loads to be transported with minimum frictional restraint.
2. DESCRIPTION OF THE PRIOR ART
To assist the storage and transport of material, common wooden pallets measuring 48 .times. 40 inches and weighing approximately 50 pounds support loads which are transported by conventional fork lift equipment, in which the fork lift operator moves the fork beneath the pallet and the overlying load and lifts the pallet and load sufficiently to permit by means of the fork lift vehicle, movement of the pallet and its load from location to location.
Wooden pallets last roughly three years, have sharp corners and after rough usage nails are exposed and broken boards which damage the loads carried thereby. The pallet itself is of a weight and configuration such that it is somewhat difficult for a single man to handle the same. Further, with the pallet being nonflexible in size, space for storage and transport of the load and the pallet is determined by the pallet size, rather than load size or available space in the transport vehicle. Further, in the trucking industry, each trucker is responsible to remove his load from the truck to the customer's tail gate or from the customer's pick up and customer's tail gate, and place it on the particular truck. Of necessity, a trucker's helper is required on all trucks since it is impossible for the trucker alone to readily move the goods to and from the truck. Further, the common fork lift is generally too heavy to move into the tractor trailer itself since it breaks through the floor of the same and therefore in many cases hand loading and unloading operations are required in which the trucker or his helper is required to employ a hand dolly. Even where the load may be retained on the pallet and a fork lift truck or the like moves the pallet and the load into the tractor trailer or the box car for rail transportation, the pallets weight of 50 pounds, takes up a good portion of the load, and additionally, each takes a portion of the space permitted by occupancy of the load, greatly increasing the cost of transporting of material. While pallets are uniform in nature, and cost approximately $5.00 new, since the pallets are shipped from location to location and generally exchanged, one shipper who ships on new pallets may recover in their place used pallets which are close to the end of their useful life.
In spite of the difficulties in employing wooden pallets, transport systems today are generalized in terms of the use of the pallet. For instance, in 1970, more than 100,000,000 wooden pallets were sold, having a general lift expectancy of three years, in spite of the deficiencies of the same as outlined above.
One of the additional disadvantages of the wooden pallet material handling system, is the fact that, in every case, the load including the pallet supporting the same must be raised above the floor prior to further lateral movement by the transport vehicle from position to position.
In an attempt to reduce the work necessary in moving palletized loads, pallets have been modified to incorporate ground effect machines, whereby, the application of superatmospheric air in the form of an air bearing or film between the bottom of the pallet and the floor supporting the same, has practically eliminated the friction between the pallet, and the underlying floor. This permits the load to be moved laterally along the floor or other support surface on an air film in a relatively frictionless manner. However, known air cushion pallets have necessarily required relatively bulky and heavy means for supplying the pressurized air and, in which case, the decrease in the frictional restraint by the presence of the air film has been more than balanced by the complexity and added load of the pressurized air generating equipment. Further, in the known air cushion pallets, the air cushion established by the pressurized air between the bottom surface of the pallet and the underlying support such as the floor may be maintained only where there is continuity in the floor surface itself and the presence of cracks, or irregularities in the floor result in the loss of the air cushion and the elimination of the frictional support.
In the air cushion field, there has recently developed an air valve in which air flow is kept to a minimum and in which case, the self valving arrangement permits localized termination of the air cushion or bearing surface at irregularities or cracks within the surface over which the air cushion is moving such that the air cushion may readily ride across such cracks without appreciable increase in resistance to and without appreciable change in the air cushion of the same.
Reference to FIG. 7 illustrates an air cushion of the prior art which incorporates a self valving feature as an improvement over conventional air cushions. In this respect, the air cushion indicated generally at 410 is constituted by a rigid, rectangular manifold 412 which permits pressurized air or the like to enter a plenum chamber 414 from a source of air pressure (not shown) which is coupled to the air cushion 410 by means of a flexible hose or the like as at 416, terminating at rigid nipple 418 constituting a flow passage to the manifold 412. Chamber 414 is further defined by the manifold 412, and a two layer flexible, composite wall 420, the bottom surface of which is constituted by an inner perforated wall 422 and an outer perforated wall 424, the perforations 426 of the inner wall being laterally offset with respect to the perforations 428 of the outer wall with the perforated walls 422 and 424 forming a plurality of check valves, which act to stop the loss of air from within the chamber 414 to the exterior surface of layer or wall 424, unless the plenum pressure within chamber 414 is substantially equal to the pressure outside of the outer fabric layer 424. This condition exists only when an air bearing is formed between the surface of the outer wall 424 and the underlying support, in this case, floor 430. When the device crosses a void such as a ditch 432 within floor 430, each sectional area of the multi-layer composite flexible wall 420 closes as the device proceeds across the ditch 432 for instance from left to right, due to the pressure differential that occurs between plenum 412 and the localized exterior as defined by the ditch 432. It is noted, however, that all areas which are not over the void or ditch 432 are supplying air to the air bearing indicated at A on each side of the ditch 432.